Series parallel transformer winding arrangement



vMarch 26, 1963 M. A. SPURWAY SERIES PARALLEL TRANSFORMER WINDING ARRANGEMENT Filed D80. 7. 1960 3 Sheets-Sheet 1 Inventor Mnugzca A. SPURu/Ay K By M Maw 7% ys March 26, 1963 M. A. SPURWAY 3, 3,3

SERIES PARALLEL TRANSFORMER WINDING ARRANGEMENT Filed D80. 7, 1960 3 Sheets-Sheet 2 F/GJ.

WW fL T L o I C /5/4 /J/2// lnvenlor MA URICE A. SPURWAY Attorneys March 26, 1963 M. A. SPURWAY 3,083,331

SERIES PARALLEL TRANSFORMER WINDING ARRANGEMENT Filed Dec. -7. 1960 3 Sheets-Sheet 3 Inventor MAIL/RICE A. SPURWAY its 3,ll83,331 SERIES PARALLEL TRANSFGPMER WlNDlNG ARRANGEMENT Maurice Alec Spurway, Manchester, England, assignor to Ferrantl, Limited, Lancasliire, England, a company of the United Kingdom of Great Britain and Northern Ireland Filed Dec. 7, 1960, Ser. No. 74,322 Claims priority, application Great Britain Dec. 16, 1959 8 (Ilaims. (Ql. 32349) This invention relates to voltage control apparatus.

More particularly, although not specifically, the invention relates to voltage control apparatus for use where the voltage has to be controlled on load under conditions of large current flow, such as, for example, in the control of the electrical supply to electric furnaces.

According to the present invention voltage control apparatus includes a transformer having a primary winding and a secondary winding, one of said windings being formed by first and second equal separate sections each having a like plurality of tappings and disposed in corresponding manner on the core of the transformer such that under all conditions the leakage impedance of corresponding parts of said sections with respect to the other winding are equal, and control means for making cross-connections between a corresponding end of each one of said sections and any corresponding one of said tappings on the other of said sections whereby in operation said sections may be progressively varied from a wholly electrical series connection with each other to a wholly electrical parallel connection with each other, and vice versa, through intermediate positions in which any portion of said first section, measured from said corresponding end to any one of the rappings on said first section, is electrically connected in parallel with a like portion of said second section, the remaining portion of each section being in electrical series connection with the portions electrically connected in parallel.

Each of said sections may have a further winding connected to said corresponding end, said further windings having a plurality of tappings to which said cross-connections may be made by said control means whereby the range of voltage control of said apparatus may be extended.

Said control means may include first and second pairs of series connected variable impedances, first switching means for connecting said first pair of impedances across any two adjacent tappings on said first section, second switching means for connecting said second pair of impedances across two corresponding adjacent tappings on said second section, the common points of said first and second pairs or" impedances being connected to said corresponding ends of said second and first sections respectively, and means for difierentially varying the value of the impedances in each pair from a high value to a low value and vice versa.

The two impedances of said first and second pairs of impedances may be formed by the two fixed coils of a moving coil voltage regulator, said means for differentially varying the value of the impedances being the moving coil of said regulator.

The present invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURES 1A, 1B and 1C are schematic drawings showing voltage control apparatus in accordance with the invention,

FIGURES 2A and 2B are schematic drawings showing a modification of the apparatus shown in FIGURES 1A, 1B and 1C,

FIGURE 3 is a sectional elevation of the windings of 3,083,331 Patented Mar. 26, 153 63 the transformer used in the circuit of FIGURES 1A, 1B and 1C, and

FIGURE 4 is a circuit diagram of one practical form of voltage control apparatus in accordance with the invention.

Referring now to FIGURES 1A, 1B and 1C there is shown a transformer having a primary winding formed by first and second equal separate sections 21 and 22, and a secondary winding 23. The section 21 has seven tappings l to 7 and the section 22 has a like seven tap pings 11 to 7, i.e. the number of turns between the tappings 1 and 2 is the same as the number of turns between the tappin s l1 and 12, the number of turns between the tappings 2 and 3 is the same as the number of turns between the toppings 12 and 13, and so on. Control means, shown schematically as arrowed connectors 24 and 25, are provided, the connector 24 making a cross-connection between the end tapping '7 of the section 21 and any one of the toppings 11 to 17 on the section 22, and the connector 25 making a cross-oonnec tion between the corresponding end tapping 17 of the ection 22 and any one of the tappings 1 to 7 on the section 21.

In operation, it will be seen from FIGURE 1A that when the connectors 24 and 25 make cross-connections to tappings ll and 1 respectively the two sections 21 and 22 are wholly connected in parallel and for a given input voltage of 33,000 volts the output on the secondary winding is at a maximum of 500 volts. If now the control means are operated to progressively change the connectors 24 and 25 to make cross-connections to tappings l4 and 4 respectively (as shown in FIGURE 13) it will be seen that the portion of sections 21 between the tappings 4 and 7 is connected in parallel with a like portion of the section 22 between the tappings l4 and 17, the remaining parts of the sections 2i and 22 being connected in series with the parallel portions. As a result the output voltage is lowered to 375 volts, the output current, however, remaining the same. The control means may again be operated to change the connectors 2d and 25 to make cross-connections to tappings l7 and 7 respectively, in which position the two sections are connected wholly in series. In this position, therefore, the output voltage is reduced to a minimum of 250 volts, the output current again remaining constant.

The control means operating the connectors 24 and 25 is reversible and this particular apparatus is therefore suitable for controlling the voltage over the range from 250 to 560 volts.

The range of voltage control may be extended by utilising the apparatus shown in FEGURES 2A and 2B. The apparatus shown in FlGURES 2A and 2B is similar to that shown in FlGURES 1A, 1B and 1C and like parts have been given like reference numerals. In this apparatus the sections 21 and 22 have been extended by connecting to them further windings 26 and 27 respectively. The winding 25 has tappings 3, 9 and 1d, and the wind ing 2'7 has tappings l8, l9 and 2d.

The operation of this apparatus is similar to that described with reference to FIGURES 1A and 1B, and here the maximum voltage obtainable across the secondary winding is 590 volts which is obtained, as before, when the two sections 21 and 22 are wholly connected in parallel, as shown in FIGURE 2A. It will be seen that the windings 26 and 27 have no active part in the operation of the apparatus under these conditions. The windings 2s and 27, however, allow a lower minimum Voltage to be obtained across the secondary winding 23 when the connectors 24 and 25 make cross connections to the tappings 18, 19 and 20, and 8, 9 and 1t) respectively. In the extreme case shown in FIGURE 2B with cross-connections made to the tappings 1th and 20 the minimum voltage of 200 volts is obtained across the secondary winding 23.

With the sections 21 and 22 interconnected in the manner described above it is possible to make a considerable saving in the material from which the conductors are made, usually copper, and thereby to reduce the loss, 'known as copper loss, which is inherent in any transformer. The maximum current flow occurs in the primary winding when the sections 21 and 22 are connected as shown in FIGURE 1A. Under these conditions each of the sections 21 and 22 carries half of the maximum current. When the sections 21 and 22 are connected as shown in FIGURE they again each carry half of the maximum current, since the effective turns of the winding have been doubled and the current therefore halved. At intermediate stages, however, parts of the sections have to carry more than half of the maximum current. For example, when the cross-connections are made to the tappings 2 and 12 the parts of the sections between the tappings 1 and 2, and 11 and 12 have to carry very nearly the full maximum current, and must therefore be wound from a conductor of suitable crosssectional area. When the cross-connections are made to the tappings 3 and 13, however, the current flowing in the winding is reduced and the parts of the sections between the tappings 2 and 3 and 12 and 13 therefore have to carry less current than the parts between the tappings 1 and 2, and 1-1 and 12. They may accordingly be wound from a conductor of less cross-sectional area. Similarly the parts of the sections between tappings 3 and 4, and 13 and 14 may be wound from a conductor of less cross-sectional area than that used for the parts between the tappings 2 and 3, and 12 and 13, and so on, until finally the parts between the tappings 6 and 7, and 16 and 17 may be wound from a conductor of sufficient cross-sectional area to carry only half of the maximum current.

It will be seen that the parts of the sections 21 and 22 carry different currents under different conditions and 'it is therefore necessary that the two sections 21 and 22 are disposed in corresponding manner on the core of the transformer. That is to say the sections 21 and 22 must be disposed on the core such that under all operating conditions the leakage impedance of each corresponding part of the sections 21 and 22 (e.g. the parts between tappings 1 and 2, and 11 and 12) is the same with respect'to the secondary winding 23. FIGURE 3 shows one suitable arrangement for the windings on the core C of a transformer.

Referring now to FIGURE 4, there is shown a circuit diagram of one practical form of voltage control apparatus in accordance with the invention. The apparatus includes a transformer, as described in the previous examples, having a primary winding formed by two sections 21 and 22, and a secondary winding 23, the sections 21 and 22 having tappings 1 to 7 and 11 to 17 respectively. The tappings 1, 3, 5 and 7 of section 21 are connected to the fixed contacts of a rotary switch 28 and the tappings 2, 4 and 6 of the section 21 are connected to the fixed contacts of a rotary switch 29. Similarly, the tappings 1 -1, 13, and 17 of section 22 are connected to the fixed contacts of a rotary switch 30 and the tappings 12, 1'4 and 16 of the section 22 are connected to the fixed contacts of a rotary switch 31. in FIGURE 4, for the sake of clarity, only the tappings 1 and 2, and ,11 and .12 have been shown connected to the appropriate rotary switches.

The movable contact 320i the switch 28 is connected via switch 33 to one end of a fixed coil 34 of a moving icoil voltage regulator 35 and the movable contact 36 of switch 29 is connected via switch 37 to one end of the other fixed coil 38 of the regulator 35. The free ends of the coils 34 and 38 are each connected to the end of section 22 at tapping '17. Similarly, the movable contact 39 of switch 30 is connected via switch 40 to one end of a fixed coil 41 of a moving coil voltage regulator 42, and the movable contact 43 of switch 31 is connected via switch 44 to one end of the other fixed coil 45 of the regulator 42. The free ends of the coils 41 and 45 are each connected to the end of section 21' at the tapping 7. The regulator 35 has a moving coil 46 by means of which the impedance of each of the coils 34 and 38 may be varied in well known manner, and the regulator 42 has a moving coil 47 by means of which the impedance of the coils 41 and 45 may likewise be varied. The moving coils 46 and 47 are mechanically connected in such a manner that movement of the coils 46 and 47 causes equal variations in the impedances of the coils 34 and 41, and 38 and 45 respectively.

In operation, voltage control with the apparatus on load is achieved in the following manner. When the moving coils 46 and 47 are in the extreme positions shown in FIGURE 4 the impedances of the coils 34 and 41 are at a minimum value and the impedances of the coils 38 and 45 are at a maximum value. Therefore, with the movable contacts 32, 36, 39 and 43 in the positions shown and switches 33, 37, 40 and 44 closed, the end of the section 22 at the tapping 17 is effectively connected to the tapping 1 of section 21 and the end of the section 21 at the tapping 7 is eifectively connected to the tapping 11 of section 22. Sections 21 and 22 are therefore connected wholly in parallel (as in FIGURE 1A) and the output voltage across the secondary winding is therefore at its maximum value. If now the moving coils 46 and 47 are progressively moved towards their other extreme positions the impedances of the coils 34 and 38 and the coils 41 and 45 are varied differentially, ie, the impedances of coils 34 and Marc progressively increased to their maximum value and the impedances of coils 38 and 45 are progressively decreased to their minimum value, the output voltage across the secondary winding 23 therefore also being decreased. When the moving coils 46 and 47 reach their other extreme positions the end of the section 22 at the tapping 17 is ef- 'fectively coupled to the tapping 2 of section 21, and the end of the section 21 at the tapping 7 is eifectively connected to the tapping '12 of the section 22. With the moving coils 46 and 47 is this position (opposite to that shown in FIGURE 4) the only current flowing in the windings 34 and 41 is the magnetising current and the switches 33 and 40 may therefore be opened without any appreciable effect on the output voltage across the secondary winding 23.

With the switches 33 and 40 open the movable contacts 32 and 3 9 may he stepped to their next position and the switches 33 and 40 closed, thus connecting tappings 3 and 13 to the coils 34 and 41. If now the moving coils 46 and 47 are progressively moved to the extreme position shown in FIGURE 4, the impedances of the coils 38 and 45 are increased to their maximum value and the impedances of the coils 34 and 41 are decreased to their minimum values, the output voltage therefore being further reduced. With the moving coils in the positions shown in FIGURE 4 the only current flowing in the coils 38 and 45 is the magnetising current andthe switches 37 and 44 may now be opened and the movable contacts 36 and 43 stepped to their next positions. Now, when the switches 37 and 44 are closed, the tappings 4 and 14 are connected to the coils 38 and 45 and the moving coils 46 and 47 may again be moved to their opposite extreme positions to further reduce the output voltage.

It will be seen that this process may be repeated along the whole of the sections 21 and 22, and since the movement of the moving coils 46 and 47 and the directions of rotation of the movable contacts 32, 36, 39' and 43 are reversible the apparatus gives complete voltage control over a given range. Furthermore, since the variation in the impedances of the coils 34, 38, 41 and 45 is stepless, the voltage control is also stepless.

The control means formed by the moving coil voltage regulators 35 and 42, and the rotary switches 28, 29, 30 and 31 may be replaced by other forms of control means. For example, in FIGURE 4, four scaturable reactors could replace the regulators 35 and 42, the saturable reactors being connected in the circuit in place of the fixed coils 34, 38, 41 and 45, means being provided for varying the direct current supplied to the control windings of each of the reactors such that the impedances of the reactors is varied in a manner similar to the manner in which the impedances of the fixed coils 34, 38, 41 and 45 is varied.

The voltage control apparatus has been described above as having the primary winding of the transformer formed by two equal separate sections and it will be seen that this provides a variable voltage output at constant current. If desired, the secondary winding may be formed by two equal separate sections instead of the primary winding, and the apparatus then provides a variable voltage output at constant volt amperes.

For the sake of simplicity the voltage control apparatus has been described and illustrated in respect of single phase alternating current. It will be appreciated, however, that the apparatus is suitable for use with two or more phase alternating current, the apparatus described above being repeated for each phase of the alternating current.

What I claim is:

1. Voltage control apparatus including a transformer having a primary winding and a secondary winding, one of said windings being formed by first and second equal separate sections each having a like plurality of tappings and disposed in corresponding manner on the core of the transformer such that under all conditions the leakage impedance of corresponding parts of said sections with respect to the other winding are equal, and control means for making cross-connections between a corresponding end of each one of said sections and any corresponding one of said tappings on the other of said sections whereby in operation said sections may be progressively varied from a wholly electrical series connection with each other to a wholly electrical parallel connection with each other, and vice versa, through intermediate positions in which any portion of said first section, measured from said corresponding end to any of the tappings on said first section, is electrically connected in parallel with a like portion of said second section, the remaining portion of each section being in electrical series connection with the por tions electrically connected in parallel.

2. Voltage control apparatus as claimed in claim 1 in which each of said sections has a further winding connected to said corresponding end, said further windings having a like plurality of tappings to which said crossconnections may be made by said control means whereby the range of voltage control of said apparatus may be extended.

3. Voltage control apparatus as claimed inclaim 1 in which said control means include first and second pairs of series connected variable impedances, first switching means for connecting said first pair of impedances across any two adjacent tappings on said first section, second switching means for connecting said second pair of impedances across two corresponding adjacent tappings on said second section, the common points of said first and second pairs of impedances being connected to said corresponding ends of said second and first sections respectively, and means for differentially varying the value of the impedances in each pair from a high value to a low value and vice versa.

4. Voltage control apparatus as claimed in claim 3 in which the two impedances of each of said first and second pairs of impedances are formed by the two fixed coils of a moving coil voltage regulator, said means for difierentially varying the value of the impedances being the moving coil of said regulator.

5. Voltage control apparatus as claimed in claim 4 in which the moving coils of the two regulators are mechanically interconnected in such manner that movement of the two moving coils causes equal variations in the values of the impedances of the corresponding fixed coils.

6. Voltage control apparatus as claimed in claim 3, in which each of said first and second switching means in cludes two rotary switches, the fixed contacts of one of said rotary switches being connected to alternate ones of the tappings on the appropriate section and the fixed contacts of the other of said rotary switches being connected to the remaining ones of the tappings on the appropriate section, said pairs of impedances being connected across the movable contacts of said rotary switches.

7. Voltage control apparatus as claimed in claim 6 in which a further switch is included in the connection be tween the movable contact of each rotary switch and said pairs of impedances.

8. Voltage control apparatus as claimed in claim 1 in which the cross-sectional area of coductor between each adjacent pair of tappings on said sections is varied according to the maximum current which that portion of the winding is required to carry.

References Cited in the file of this patent UNITED STATES PATENTS 1,630,363 Travers May 31, 1927 2,186,207 Rampacher Jan. 9, 1940 FOREIGN PATENTS 60,314 Sweden Dec. 16, 1924 

1. VOLTAGE CONTROL APPARATUS INCLUDING A TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING, ONE OF SAID WINDINGS BEING FORMED BY FIRST AND SECOND EQUAL SEPARATE SECTIONS EACH HAVING A LIKE PLURALITY OF TAPPINGS AND DISPOSED IN CORRESPONDING MANNER ON THE CORE OF THE TRANSFORMER SUCH THAT UNDER ALL CONDITIONS THE LEAKAGE IMPEDANCE OF CORRESPONDING PARTS OF SAID SECTIONS WITH RESPECT TO THE OTHER WINDING ARE EQUAL, AND CONTROL MEANS FOR MAKING CROSS-CONNECTIONS BETWEEN A CORRESPONDING END OF EACH ONE OF SAID SECTIONS AND ANY CORRESPONDING ONE OF SAID TAPPINGS ON THE OTHER OF SAID SECTIONS WHEREBY IN OPERATION SAID SECTIONS MAY BE PROGRESSIVELY VARIED FROM A WHOLLY ELECTRICAL SERIES CONNECTION WITH EACH OTHER TO A WHOLLY ELECTRICAL PARALLEL CONNECTION WITH EACH OTHER, AND VICE VERSA, THROUGH INTERMEDIATE POSITIONS IN WHICH ANY PORTION OF SAID FIRST SECTION, MEASURED FROM SAID CORRESPONDING END TO ANY OF THE TAPPINGS ON SAID FIRST SECTION, IS ELECTRICALLY CONNECTED IN PARALLEL WITH A LIKE PORTION OF SAID SECOND SECTION, THE REMAINING PORTION OF EACH SECTION BEING IN ELECTRICAL SERIES CONNECTION WITH THE PORTIONS ELECTRICALLY CONNECTED IN PARALLEL. 